1. Field of the Invention
The present invention relates to a rubber member for a paper feed device, more particularly to a rubber member which is outstandingly effective when used as a duplicate feed preventive rubber pad or rubber roller for separating and feeding sheets of paper smoothly, one by one in a paper feed device of copier, facsimile apparatus, printer or other office automating equipment.
2. Prior Art
In a paper feed device for a copier, facsimile apparatus, printer or other office automating equipment, in order to feed multiple sheets of paper set up in a stack-up state in a cassette or the like by separating one by one, the roller/pad separating method as shown in FIG. 1, the roller/roller separating method as shown in FIG. 2 or other separating mechanism is provided. In FIG. 1 and FIG. 2, numerals 1, 2 and 3 respectively, denote sheets of paper, a paper feed roller, and a rubber pad or rubber roller as duplicate feed preventive rubber member.
Using the paper feed rubber roller 2 and duplicate feed preventive rubber member 3, in order to feed multiple sheets of paper 1, 1 . . . set in a stack-up state in a cassette (not shown) or the like smoothly by separating one by one, it is required that the friction coefficient between members should satisfy the following formula 1. EQU .mu.F&gt;.mu.R&gt;.mu.P Formula 1
where .mu.F is the friction coefficient between feed roller 2 and paper 1, .mu.R is the friction coefficient between duplicate feed preventive rubber member 3 and paper 1, and .mu.P is the friction coefficient between sheets of paper 1, 1.
This relation must be maintained even after passing at least 100,000 sheets.
As a result of measurement of .mu.F and .mu.P in actually used members, .mu.F was 1.5 to 2.5 and .mu.F was 0.3 to 0.6, and hence .mu.R is desired to be somewhere between 0.7 and 1.2. In the case of a film for an OHP (overhead projector), .mu.F is 2.5 to 3.0 and .mu.P is 0.3 to 1.5, and hence .mu.R should be 1.7 to 2.4.
Hitherto, the duplicate feed preventive rubber member 3 is composed of, as a substance excellent in wear resistance, urethane, combination of urethane and cork, natural rubber, chloroprene, or the like.
In the conventional duplicate feed preventive rubber member 3 composed of urethane, combination of urethane and cork, natural rubber, chloroprene or the like, when sliding on the paper 1, the paper 1 is electrically charged, and an electrostatic image disturbance occurs in the transfer step in the electrophotographic process. In the electrophotographic progress, generally, for example in the electrophotographic apparatus as shown in FIG. 3, after the surface of a photosensitive drum 4 is uniformly charged by a charger 5, an optical image of the original is projected. The electric charge disappears in the illuminated portion, thereby forming an electrostatic latent image (an invisible electric image) on the surface of this photosensitive drum 4, and a toner (the developer) is pulled out from a toner tank of a developing roller 6 to deposit on the charged portion of the surface of the photosensitive drum 4. The toner on the surface of the photosensitive drum 4 is transferred on the paper 1, electrically charged by a transfer charger 7, then the toner image transferred on the paper 1 is passed through two rollers (not shown) to be fixed thermally (about 160.degree. to 200.degree. C.). On the other hand, generally, when the paper 1 onto rubber member 3 slide on each other, the paper 1 is positively charged, while the rubber member 3 is negatively charged. In this mechanism of electrophotographic apparatus, when using a toner of negative electric charge, if the paper 1 is positively charged, it may attract the toner of negative charge on the surface of the photosensitive drum 4 before transfer as shown in FIG. 4, which may result in image disturbance.
It may be therefore considered to make the rubber compositive conductive so as not to charge by blending the polymer with carbon black or conductive zinc white, but if the carbon black is blended sufficiently so as to be conductive, when sliding on the paper 1, the paper 1 may be stained, and it is not suited as the duplicate feed preventive rubber member 2. Or if the conductive zinc white is blended enough to be conductive, the wear resistance is impaired, and it is not suited as the duplicate feed preventive rubber member used in severe abrasive condition of sliding against the paper 1.